Growth of new cells in brain erases old memories: Study

Toronto: If you could not make sense of a childhood story that your parents and neighbours related, you are not alone. Childhood memories do fade and researchers have found that growth of new cells in brain could erase old memories to make way for new ones.

Newly-formed neurons in the hippocampus (an area of the brain involved in memory formation) could dislodge previously learned information, said the study.

"Memory is based on a circuit, so if you add to this circuit, it makes sense that it would disrupt it," said Sheena Josselyn, a neuroscientist at the Hospital for Sick Children in Toronto, Canada.

However, growth of new brain cells is associated with increased capacity to learn new memories in the future.

For the study, researchers tested newborn and adult mice on a conditioning task, training the animals to fear an environment in which they received repeated electric shocks.

All the mice learned the task quickly, but whereas infant mice remembered the negative experience for only one day after training, adult mice retained the negative memory for several weeks. This difference seemed to correlate with differences in neural proliferation.

The researchers were able to enhance memory persistence in newborn mice by genetically and chemically suppressing growth of new neurons after learning. And in adult mice, four to six weeks of regular exercise - an activity known to promote neuron proliferation - reduced the persistence of previously learned fear.

As both mice and humans have 'infantile amnesia', or pronounced forgetting of early life experiences, the findings could hold true even for humans. The study appeared in the journal Science.